Celestron AstroMaster LT 76AZ Owner's manual

Brand: Celestron

Model: AstroMaster LT 76AZ

Category: Telescopes

Type: Owner's manual

This manual is also suitable for

Series Telescopes

INSTRUCTION MANUAL

• AstroMaster

LT 60AZ # 21073 • AstroMaster

LT 70AZ # 21074

• AstroMaster

LT 76AZ # 31036

AstroMaster

LT 60AZ

AstroMaster

LT 76AZ

TABLE OF CONTENTS

INTRODUCTION ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 3

ASSEMBLY ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 6

Setting up the Tripod •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 6

Moving the Telescope Manually ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 7

Attaching the Telescope Tube to the Mount •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 7

Installing the Diagonal & Eyepieces (refractor) ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 8

Installing the Eyepieces on the Newtonians •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 8

TELESCOPE BASICS ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 9

Image Orientation •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 10

Focusing •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 10

Aligning the Finderscope ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••10

Calculating Magniﬁcation ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 11

Determining Field of View •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12

General Observing Hints •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12

ASTRONOMY BASICS •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13

The Celestial Coordinate System •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13

Motion of the Stars ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 14

CELESTIAL OBSERVING ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Observing the Moon ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Observing the Planets •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Observing the Sun ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Observing Deep Sky Objects •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 16

Seeing Conditions •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 18

ASTROPHOTOGRAPHY••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 19

Short Exposure Prime Focus Photography •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 19

Planetary & Lunar Photography with Special Imagers ••••••••••••••••••••••••••••••••••••••••••••••••• 19

CCD Imaging for Deep Sky Objects ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 19

Terrestrial Photography •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 19

TELESCOPE MAINTENANCE •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 20

Care and Cleaning of the Optics •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 20

Collimation of a Newtonian •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 20

AstroMaster LT Speciﬁcations••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 24

Congratulations on your purchase of an AstroMaster LT Series telescope. The AstroMaster LT Series of

telescopes come in several different models and this manual covers three models mounted on the Alt-AZ

Mount (an altazimuth is the simplest type of mount with two motions – altitude (up & down) and azimuth

(side-to-side))-- 60mm refractor, 70mm refractor, and 76mm Newtonian. The AstroMaster LT Series is

made of the highest quality materials to ensure stability and durability. All this adds up to a telescope that

gives you a lifetime of pleasure with a minimal amount of maintenance.

These telescopes were designed for the First Time Buyer offering exceptional value. The AstroMaster LT

series features a compact and portable design with ample optical performance to excite any newcomer to

the world of amateur astronomy. In addition, your AstroMaster LT telescope is ideal for terrestrial obser-

vations which will open your eyes with superb high power viewing.

AstroMaster LT telescopes carry a two year limited warranty. For details see our website at

www.celestron.com

Some of the many standard features of the AstroMaster LT include:

• All coated glass optical elements for clear, crisp images.

• Smooth functioning, rigid alt-azimuth mount with a large pan handle with built-in clutch for

easy targeting.

• Preassembled steel leg tripod with 1” legs ensures stable platform.

• Quick and easy no-tool set up.

• CD-ROM “The Sky X” Level 1 --- astronomy software which provides education about the sky

and print able sky maps.

• All models can be used terrestrially as well as astronomically with the standard accessories included.

Take time to read through this manual before embarking on your journey through the Universe. It may

take a few observing sessions to become familiar with your telescope, so you should keep this manual

handy until you have fully mastered your telescope’s operation. The manual gives detailed information re-

garding each step as well as needed reference material and helpful hints guaranteed to make your observ-

ing experience as simple and pleasurable as possible.

Your telescope is designed to give you years of fun and rewarding observations. However, there are a few

things to consider before using your telescope that will ensure your safety and protect your equipment.

Warning

• Never look directly at the sun with the naked eye or with a telescope (unless you have the proper solar

ﬁlter). Permanent and irreversible eye damage may result.

• Never use your telescope to project an image of the sun onto any surface. Internal heat build-up can

damage the telescope and any accessories attached to it.

• Never use an eyepiece solar lter or a Herschel wedge. Internal heat build-up inside the telescope can

cause these devices to crack or break, allowing unﬁltered sunlight to pass through to the eye.

• Do not leave the telescope unsupervised, either when children are present or adults who may not be

familiar with the correct operating procedures of your telescope.

INTRODUCTION

1. Objective Lens

2. Telescope Optical Tube

3. Star Pointer Finderscope

4. Eyepiece

5. Diagonal

6. Focus Knob

7. Pan Handle

8. Accessory Tray

9. Tripod

10. Azimuth Lock

11. Alt-Az Mount

12. Dovetail Mounting Bracket

Figure 1-1 AstroMaster LT 70AZ Refractor

(AstroMaster LT 60AZ refractor similar)

1. Star Pointer Finderscope

2. Eyepiece

3. Telescope Optical Tube

4. Primary Mirror

5. Pan Handle

6. Azimuth Lock

7. Accessory Tray

8. Tripod

9. Alt-Az Mount

10. Dovetail Mounting Bracket

11. Focus Knob

Figure 1-2 AstroMaster LT 76 AZ Newtonian

This section covers the assembly instructions for your AstroMaster LT telescope. Your telescope should be

set up indoor the ﬁrst time so that it is easy to identify the various parts and familiarize yourself with the

correct assembly procedure before attempting it outdoor.

Each AstroMaster LT comes in one box. The pieces in the box are – optical tube with attached sky pointer ,

Alt-Az mount with attached pan handle, 10 mm eyepiece – 1.25”, 20 mm eyepiece – 1.25”, mirror diagonal

1.25” (for 60AZ and 70 AZ), “The Sky” Level 1 CD-ROM.

SETTING UP THE TRIPOD

1. Remove the tripod from the box (Figure 2-1). The tripod comes preassembled so that the set up is very

easy.

2. Stand the tripod upright and pull the tripod legs apart until each leg is fully extended and then push

down slightly on the tripod leg brace (Figure 2-2). The very top of the tripod is called the tripod head.

3. Next, we will install the tripod accessory tray (Figure 2-3) onto the tripod leg brace

(center of Figure 2-2).

4. Insert the cut-out in the center of the tray (ﬂat side of the tray facing down) to match the center of the

tripod leg brace and push down slightly (Figure 2-4). The ears of the tray should appear as in Figure 2-4

5. Rotate the tray until the ears are under the leg brace support of each leg and push slightly and they will

lock in place (Figure 2-5). The tripod is now completely assembled (Figure 2-6).

6. You can extend the tripod legs to the height you desire. At the lowest level the height is 24” (61cm)

and extends to 41” (104cm). You unlock the tripod leg lock knob at the bottom of each leg (Figure 2-7)

and pull the legs out to the height you want & then lock the knob securely. A fully extended the tripod

looks like the image in Figure 2-8.

7. The tripod will be the most rigid and stable at the lowest height.

ASSEMBLY

Figure 2-1 Figure 2-3 Figure 2-2 Figure 2-4

Figure 2-5 Figure 2-7 Figure 2-6 Figure 2-8

MOVING THE TELESCOPE MANUALLY

The AstroMaster LT Alt-Az mount is easy to move wherever you want to point it. The up and down (altitude)

is controlled by the pan handle (Figure 2-10). The side-to-side (azimuth) is controlled by the azimuth lock

(Figure 2-9). The pan handle and the azimuth lock are both loosened by turning the handle and lock coun-

terclockwise. When loose you can ﬁnd your objects easily and then lock the controls. To lock the controls

in place, turn them clockwise.

ATTACHING THE TELESCOPE TUBE TO THE MOUNT

The telescope optical tube attaches to the mount via a dovetail slide bar mounting bracket at the top of the

mount (Figure 2-11). The mounting bar is attached along the bottom of the telescope tube. Before you

attach the optical tube, make sure that the pan handle and azimuth lock are fully locked. Then put the

dovetail bracket in the horizontal position as shown in Figure 2-10. This will ensure that the mount does not

move suddenly while attaching the telescope optical tube. Also, remove the objective lens cap (refractor) or

the front opening cap (Newtonian). To mount the telescope tube:

1. Remove the protective paper covering the optical tube.

2. Loosen the mounting knob and the mounting safety screw on the side of the dovetail mounting platform

so they do not protrude into the mounting platform – see Figure 2-11.

3. Slide the dovetail mounting bar into the recess on the top of the mounting platform (ﬁgure 2-12).

4. Tighten the mounting knob on the dovetail mounting platform to hold the telescope in place.

5. Hand tighten the mounting platform safety screw until the tip touches the side of the mounting bracket.

NOTE: Never loosen any of the knobs

on the telescope tube or mount other

than the pan handle and azimuth locks.

Mounting Knob & Safety Screw

in the dovetail bracket.

Shown is the 90AZ telescope tube

Figure 2-9

Figure 2-11 Figure 2-12

Figure 2-10

INSTALLING THE DIAGONAL & EYEPIECES ( REFRACTOR)

The diagonal is a mirror assembly that diverts the light at a right angle to the light path of the refractor.

This allows you to observe in a position that is more comfortable than if you looked straight through.

Also, the diagonal can be rotated to any position which is most favorable for you. To install the diagonal

and eyepieces:

1. Insert the small barrel of the diagonal into the 1.25” eyepiece

adapter of the focus tube on the refractor – Figure 2-13. Make sure

the two thumbscrews on the eyepiece adapter do not protrude into the

focuser tube before installation and the plug up cap is removed from

the eyepiece adapter.

2. Put the chrome barrel end of one of the eyepieces into the diagonal

and tighten the thumb screw. Again, when doing this make sure the

thumb screw is not protruding into the diagonal before inserting

the eyepiece.

3. The eyepieces can be changed to other focal lengths by reversing

the procedure in step 2 above.

INSTALLING THE EYEPIECES ON THE NEWTONIANS

The eyepiece (or ocular) is an optical element that magniﬁes the image

focused by the telescope. Without the eyepiece it would be impossible

to use the telescope visually. Eyepieces are commonly referred to by

focal length and barrel diameter. The longer focal length (i.e., the larger

the number) the lower the eyepiece magniﬁcation (i.e., power). Gen-

erally, you will use low-to-moderate power when viewing. For more

information on how to determine power, see the section on “Calculating

Magnication”. The eyepiece ts directly into the focuser of the Newto-

nians. To attach the eyepieces:

1. Make sure the thumbscrews are not protruding into the focuser tube.

Then, insert the chrome barrel

of the eyepieces into the focus tube (remove the plug up cap of the

focuser ﬁrst) and tighten the thumbscrews – see Figure 2-14.

2. The eyepieces can be changed by reversing the procedure as described above.

Figure 2-13

Figure 2-14

A telescope is an instrument that collects and focuses light. The nature of the optical design determines

how the light is focused. Some telescopes, known as refractors, use lenses, .and other telescopes, known

as reﬂectors (Newtonians), use mirrors.

Developed in the early 1600s, the refractor is the

oldest telescope design. It derives its name from

the method it uses to focus incoming light rays.

The refractor uses a lens to bend or refract incom-

ing light rays, hence the name (see Figure 3-1).

Early designs used single element lenses. How-

ever, the single lens acts like a prism and breaks

light down into the colors of the rainbow, a phe-

nomenon known as chromatic aberration. To get

around this problem, a two-element lens, known

as an achromat, was introduced. Each element has

a different index of refraction allowing two differ-

ent wavelengths of light to be focused at the same

point. Most two-element lenses, usually made of

crown and ﬂint glasses, are corrected for red and

green light. Blue light may still be focused at a

slightly different point.

A Newtonian reﬂector uses a single concave mir-

ror as its primary. Light enters the tube traveling

to the mirror at the back end. There light is bent

forward in the tube to a single point, its focal point.

Since putting your head in front of the telescope to

look at the image with an eyepiece would keep the

reﬂector from working, a ﬂat mirror called a diago-

nal intercepts the light and points it out the side of

the tube at right angles to the tube. The eyepiece

is placed there for easy viewing.

Newtonian Reﬂector telescopes replace heavy

lenses with mirrors to collect and focus the light,

providing much more light-gathering power for

the money spent. Because the light path is inter-

cepted and reﬂected out to the side, you can have

focal lengths up to 1000mm and still enjoy a

telescope that is relatively compact and portable.

A Newtonian Reﬂector telescope offers such impressive

light-gathering characteristics you can take a serious

interest in deep space astronomy even on a modest

budget. Newtonian Reﬂector telescopes do require

more care and maintenance because the primary

mirror is exposed to air and dust. However, this

small drawback does not hamper this type of

telescope’s popularity with those who want an

economical telescope that can still resolve faint,

distant objects.

Figure 3-1

A cutaway view of the light path of the

Refractor optical design

Figure 3-1

Cutaway view of the light path of the Newtonian

TELESCOPE BASICS

IMAGE ORIENTATION

The image orientation changes depending on how the eyepiece is inserted into the telescope. When using

a star diagonal with refractors, the image is right-side-up, but reversed from left-to-right (i.e., mirror im-

age). If inserting the eyepiece directly into the focuser of a refractor (i.e., without the diagonal), the image

is upside-down and reversed from left-to-right (i.e., inverted).

Newtonian reﬂectors produce a right-side-up image but the image will appear rotated based on the loca-

tion of the eyepiece holder in relation to the ground.

FOCUSING

To focus your refractor or Newtonian telescope, simply turn the focus knob located directly below the eye-

piece holder (see Figures 1-1 and 1-2). Turning the knob clockwise allows you to focus on an object that is

farther than the one you are currently observing. Turning the knob counterclockwise from you allows you

to focus on an object closer than the one you are currently observing.

Note: If you wear corrective lenses (speciﬁcally glasses), you may want to remove them when observing

with an eyepiece attached to the telescope. However, when using a camera you should always wear correc-

tive lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn

at all times.

ALIGNING THE FINDERSCOPE

The Star Pointer is the quickest and easiest way to point your telescope exactly at a desired object in the

sky. It’s like having a laser pointer that you can shine directly onto the night sky. The Star Pointer is a zero

magniﬁcation pointing tool that uses a coated glass window to superimpose the image of a small red dot

onto the night sky. While keeping both eyes open when looking through the Star Pointer, simply move your

telescope until the red dot, seen through the Star Pointer, merges with the object as seen with your unaided

eye. The red dot is produced by a light-emitting diode (LED); it is not a laser beam and will not damage the

glass window or your eye. The star pointer is powered by a long life 3-volt lithium battery (#CR1620) see

Figure 3-4. Like all ﬁnderscopes, the Star Pointer must be properly aligned with the main telescope before it

can be used. The alignment procedure is best done at night since the LED dot will be difﬁcult to see during

the day.

Image orientation as seen with the

unaided eye & using erecting de-

vices on refractors & Newtonians

Figure 3-3

Reversed from left to right, as

viewed using a Star Diagonal on

a refractor

Inverted image, normal with

Newtonians & as viewed with

eyepiece directly in a refractor

To align the Star Pointer ﬁnderscope:

1. To turn on the Star Pointer, turn the switch to the “on” position – see Figure 3-4.

2. Locate a bright star or planet and center it in a low power eyepiece in the main telescope.

3. With both eyes open, look through the glass window at the alignment star.

If the Star Pointer is perfectly aligned, you will see the

red LED dot overlap the alignment star. If the Star Pointer

is not aligned, take notice of where the red dot is relative

to the bright star.

4. Without moving the main telescope, turn the Star

Pointer’s two adjustment screws until the red dot is

directly over the alignment star. Experiment as to which

way each screw moves the red dot.

5. The Star Pointer is now ready for use. Always turn

the power off after you have found an object. This

will extend the life of both the battery and the LED.

Note: Your battery may be installed already. If not, open the

battery compartment – see Figure 3-4 with a thin coin or

screwdriver. Put the battery in with the “+” sign facing out.

Then put the battery compartment back on. If you ever need

to replace the battery, it is a 3-volt lithium type # CR 1620.

Note: The above description applies basically for astronomy. If your ﬁnderscope

is aligned properly, you can use it for terrestrial applications also. The ﬁnderscope

acts like a sighting tube. The red dot may be difﬁcult to see in the daytime but the

dot will let you align objects before looking through the main telescope optics and

can be quite helpful.

CALCULATING MAGNIFICATION

You can change the power of your telescope just by changing the eye-

piece (ocular). To determine the magniﬁcation of your telescope, simply

divide the focal length of the telescope by the focal length of the eyepiece

used. In equation format, the formula looks like this:

Focal Length of Telescope (mm)

Magniﬁcation =

Focal Length of Eyepiece (mm)

Let’s say, for example, you are using the 20mm eyepiece that came with your telescope. To determine the

magniﬁcation you simply divide the focal length of your telescope (the AstroMaster LT 60AZ for this example

has a focal length of 700mm) by the focal length of the eyepiece, 20mm. Dividing 700 by 20 yields a magniﬁ-

cation of 35 power.

Although the power is variable, each instrument under average skies has a limit to the highest useful mag-

niﬁcation. The general rule is that 60 power can be used for every inch of aperture. For example, the Astro-

Master LT 60AZ is 2.4” inches in diameter. Multiplying 2.4 by 60 gives a maximum useful magnication of

144 power. Although this is the maximum useful magniﬁcation, most observing is done in the range of 20 to

35 power for every inch of aperture which is 48 to 84 times for the AstroMaster LT 60AZ telescope. You can

determine the magniﬁcation for your telescope the same way.

Figure 3-5

Figure 3-4

Battery

Compartment

On/Off

Switch

DETERMINING FIELD OF VIEW

Determining the ﬁeld of view is important if you want to get an idea of the angular size of the object you are

observing. To calculate the actual ﬁeld of view, divide the apparent ﬁeld of the eyepiece (supplied by the

eyepiece manufacturer) by the magniﬁcation. In equation format, the formula looks like this:

Apparent Field of Eyepiece

True Field =

Magniﬁcation

As you can see, before determining the ﬁeld of view, you must calculate the magniﬁcation. Using the ex-

ample in the previous section, we can determine the ﬁeld of view using the same 20mm eyepiece that is

supplied standard with the AstroMaster LT 60AZ telescope. The 20mm eyepiece has an apparent ﬁeld of

view of 50°. Divide the 50° by the magniﬁcation, which is 30 power. This yields an actual ﬁeld of 1.7°.

To convert degrees to feet at 1,000 yards, which is more useful for terrestrial observing, simply multiply by

52.5. Continuing with our example, multiply the angular ﬁeld of 1.7° by 52.5. This produces a linear ﬁeld

width of 89 feet at a distance of one thousand yards.

GENERAL OBSERVING HINTS

When working with any optical instrument, there are a few things to remember to ensure you get the best

possible image.

• Never look through window glass. Glass found in household windows is optically imperfect, and as

a result, may vary in thickness from one part of a window to the next. This inconsistency can and will

affect the ability to focus your telescope. In most cases you will not be able to achieve a truly sharp

image, while in some cases, you may actually see a double image.

• Never look across or over objects that are producing heat waves. This includes asphalt parking lots on

hot summer days or building rooftops.

• Hazy skies, fog, and mist can also make it difcult to focus when viewing terrestrially. The amount of

detail seen under these conditions is greatly reduced.

• If you wear corrective lenses (specically glasses), you may want to remove them when observing

with an eyepiece attached to the telescope. When using a camera, however, you should always wear

corrective lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses

must be worn at all times.

Up to this point, this manual covered the assembly and basic operation of your telescope. However, to un-

derstand your telescope more thoroughly, you need to know a little about the night sky. This section deals

with observational astronomy in general and includes information on the night sky and polar alignment.

For telescopes with equatorial mounts, the users have setting circles and polar alignment methods to help

them nd objects in the sky. With your altazimuth mount, you can use a method called “star hopping”

which is described in the “Celestial Observing Section” later in this manual. Good star maps are essential in

helping you locate deep sky objects and current monthly astronomy magazines will help you locate where

the planets are.

THE CELESTIAL COORDINATE SYSTEM

To help ﬁnd objects in the sky, astronomers use a

celestial coordinate system that is similar to our

geographical co-ordinate system here on Earth.

The celestial coordinate system has poles, lines

of longitude and latitude, and an equator. For the

most part, these remain ﬁxed against the back-

ground stars.

The celestial equator runs 360 degrees around

the Earth and separates the northern celestial

hemisphere from the southern. Like the Earth’s

equator, it bears a reading of zero degrees.

On Earth this would be latitude. However, in the sky

this is referred to as declination, or DEC for short.

Lines of declination are named for their angular

distance above and below the celestial equator.

The lines are broken down into degrees, minutes

of arc, and seconds of arc. Declination readings

south of the equator carry a minus sign (-) in front

of the coordinate and those north of the celestial

equator are either blank (i.e., no designation) or

preceded by a plus sign (+).

The celestial equivalent of longitude is called Right Ascension, or R.A. for short. Like the Earth’s lines of lon-

gitude, they run from pole to pole and are evenly spaced 15 degrees apart. Although the longitude lines are

separated by an angular distance, they are also a measure of time. Each line of longitude is one hour apart

from the next. Since the Earth rotates once every 24 hours, there are 24 lines total. As a result, the R.A.

coordinates are marked off in units of time. It begins with an arbitrary point in the constellation of Pisces

designated as 0 hours, 0 minutes, 0 seconds. All other points are designated by how far (i.e., how long) they

lag behind this coordinate after it passes overhead moving toward the west.

Figure 4-1

The celestial sphere seen from the outside

showing R.A. and DEC.

ASTRONOMY BASICS

MOTION OF THE STARS

The daily motion of the Sun across the sky is

familiar to even the most casual observer. This

daily trek is not the Sun moving as early astrono-

mers thought, but the result of the Earth’s rota-

tion. The Earth’s rotation also causes the stars

to do the same, scribing out a large circle as the

Earth completes one rotation. The size of the

circular path a star follows depends on where

it is in the sky. Stars near the celestial equator

form the largest circles rising in the east and set-

ting in the west. Moving toward the north ce-

lestial pole, the point around which the stars in

the northern hemisphere appear to rotate, these

circles become smaller. Stars in the mid-celes-

tial latitudes rise in the northeast and set in the

northwest. Stars at high celestial latitudes are

always above the horizon, and are said to be cir-

cumpolar because they never rise and never set.

You will never see the stars complete one circle

because the sunlight during the day washes out

the starlight. However, part of this circular mo-

tion of stars in this region of the sky can be seen

by setting up a camera on a tripod and opening

the shutter for a couple hours. The timed expo-

sure will reveal semicircles that revolve around

the pole. (This description of stellar motions also

applies to the southern hemisphere except all

stars south of the celestial equator move around

the south celestial pole.)

Figure 4-2

All stars appear to rotate around the celestial poles. How-

ever, the appearance of this motion varies depending on

where you are looking in the sky. Near the north celestial

pole the stars scribe out recognizable circles centered on the

pole (1). Stars near the celestial equator also follow circular

paths around the pole. But, the complete path is interrupted

by the horizon. These appear to rise in the east and set in

the west (2). Looking toward the opposite pole, stars curve

or arc in the opposite direction scribing a circle around the

opposite pole (3).

Stars seen near the

north celestial pole

Stars seen near the

celestial equator

Stare seen looking

in the opposite

direction of the

north celestial pole

With your telescope set up, you are ready to use it for observing. This section covers visual observing

hints for both solar system and deep sky objects as well as general observing conditions which will affect

your ability to observe.

OBSERVING THE MOON

Often, it is tempting to look at the Moon when it is full. At this time, the

face we see is fully illuminated and its light can be overpowering. In ad-

dition, little or no contrast can be seen during this phase.

One of the best times to observe the Moon is during its partial phases

(around the time of ﬁrst or third quarter). Long shadows reveal a great

amount of detail on the lunar surface. At low power you will be able to

see most of the lunar disk at one time. Change to optional eyepieces for

higher power (magniﬁcation) to focus in on a smaller area.

Lunar Observing Hints

To increase contrast and bring out detail on the lunar surface, use optional

ﬁlters. A yellow ﬁlter works well at improving contrast while a neutral

density or polarizing ﬁlter will reduce overall surface brightness and glare.

OBSERVING THE PLANETS

Other fascinating targets include the ﬁve naked eye planets. You can see

Venus go through its lunar-like phases. Mars can reveal a host of surface

detail and one, if not both, of its polar caps. You will be able to see the

cloud belts of Jupiter and the great Red Spot (if it is visible at the time you

are observing). In addition, you will also be able to see the moons of Jupi-

ter as they orbit the giant planet. Saturn, with its beautiful rings, is easily

visible at moderate power.

Planetary Observing Hints

• Remember that atmospheric conditions are usually the limiting factor on how much planetary detail

will be visible. So, avoid observing the planets when they are low on the horizon or when they are

directly over a source of radiating heat, such as a rooftop or chimney. See the “Seeing Conditions”

section later in this section.

• To increase contrast and bring out detail on the planetary surface, try using Celestron eyepiece lters.

OBSERVING THE SUN

Although overlooked by many amateur astronomers, solar observation is both rewarding and fun. How-

ever, because the Sun is so bright, special precautions must be taken when observing our star so as not to

damage your eyes or your telescope.

For safe solar viewing, use a solar ﬁlter that reduces the intensity of the Sun’s light, making it safe to view.

With a ﬁlter you can see sunspots as they move across the solar disk and faculae, which are bright patches

seen near the Sun’s edge.

CELESTIAL OBSERVING

• The best time to observe the Sun is in the early morning or late afternoon when the air is cooler.

• To center the Sun without looking into the eyepiece, watch the shadow of the telescope tube until

it forms a circular shadow.

OBSERVING DEEP SKY OBJECTS

Deep-sky objects are simply those objects outside the boundaries of our solar system. They include star

clusters, planetary nebulae, diffuse nebulae, double stars and other galaxies outside our own Milky Way.

Most deep-sky objects have a large angular size. Therefore, low-to-moderate power is all you need to see

them. Visually, they are too faint to reveal any of the color seen in long exposure photographs. Instead,

they appear black and white. And, because of their low surface brightness, they should be observed from a

dark-sky location. Light pollution around large urban areas washes out most nebulae making them difﬁcult,

if not impossible, to observe. Light Pollution Reduction ﬁlters help reduce the background sky brightness,

thus increasing contrast.

Star Hopping

One convenient way to ﬁnd deep-sky objects is by star hopping. Star hopping is done by using bright stars

to “guide” you to an object. For successful star hopping, it is helpful to know the eld of view of you tele-

scope. If you’re using the standard 20mm eyepiece with the AstroMaster LT telescope, your ﬁeld of view is

approximately 1º. If you know an object is 3º away from your present location, then you just need to move 3

ﬁelds of view. If you’re using another eyepiece, then consult the section on determining ﬁeld of view. Listed

below are directions for locating two popular objects.

The Andromeda Galaxy (Figure 5-1), also known as M31, is an easy target. To ﬁnd M31:

1. Locate the constellation of

Pegasus, a large square visible

in the fall (in the eastern

sky, moving toward the point

overhead) and winter

months (overhead, moving

toward the west).

2. Start at the star in the northeast

corner—Alpha (α) Andromedae.

3. Move northeast approximately

7°. There you will ﬁnd two stars

of equal brightness—Delta (δ)

and Pi (π) Andromeda—about

3° apart.

4. Continue in the same direction

another 8°. There you will ﬁnd

two stars—Beta (β) and Mu (µ)

Andromedae— als about 3°

apart.

5. Move 3° northwest—the same

distance between the two stars—

to the Andromeda galaxy.

Figure 5-1

Star hopping to the Andromeda Galaxy (M31) is a snap, since all the stars needed to do so are visible to the

naked eye.

Star hopping will take some getting used to and objects that don’t have stars near them that are visible to

the naked eye are challenging. One such object is M57 (Figure 5-2), the famed Ring Nebula. Here’s how to

ﬁnd it:

1. Find the constellation of Lyra, a small parallelogram visible in the summer and fall months. Lyra is

easy to pick out because it contains the bright star Vega.

2. Start at the star Vega—Alpha (α) Lyrae—and move a few degrees southeast to ﬁnd the parallelogram.

The four stars that make up this geometric shape are all similar in brightness, making them easy to see.

3. Locate the two southernmost stars that make up the parallelogram—Beta (β) and Gamma (γ) Lyra.

4. Point about halfway between these two stars.

5. Move about ½° toward Beta (β) Lyra, while remaining on a line connecting the two stars.

6. Look through the telescope and the Ring Nebula should be in your ﬁeld of view. The Ring Nebula’s

angular size is quite small and difﬁcult to see.

7. Because the Ring Nebula is rather faint, you

may need to use “averted vision” to see it.

“Averted vision” is a technique of looking

slightly away from the object you’re observing.

So, if you are observing the Ring Nebula, center

it in your ﬁeld of view and then look off toward

the side. This causes light from the object

viewed to fall on the black and white sensitive

rods of your eyes, rather than your eyes color

sensitive cones. (Remember that when

observing faint objects, it’s important to try to

observe from a dark location, away from street

and city lights. The average eye takes about

20 minutes to fully adapt to the darkness. So

always use a red-ﬁltered ﬂashlight to preserve

your dark-adapted night vision).

These two examples should give you an idea

of how to star hop to deep-sky objects. To use

this method on other objects, consult a star

atlas, then star hop to the object of your choice

using “naked eye” stars.

Figure 5-2

SEEING CONDITIONS

Viewing conditions affect what you can see through your telescope during an observing session. Condi-

tions include transparency, sky illumination, and seeing. Understanding viewing conditions and the effect

they have on observing will help you get the most out of your telescope.

Transparency

Transparency is the clarity of the atmosphere which is affected by clouds, moisture, and other airborne

particles. Thick cumulus clouds are completely opaque while cirrus can be thin, allowing the light from

the brightest stars through. Hazy skies absorb more light than clear skies making fainter objects harder to

see and reducing contrast on brighter objects. Aerosols ejected into the upper atmosphere from volcanic

eruptions also affect transparency. Ideal conditions are when the night sky is inky black.

Sky Illumination

General sky brightening caused by the Moon, aurorae, natural airglow, and light pollution greatly affect

transparency. While not a problem for the brighter stars and planets, bright skies reduce the contrast of

extended nebulae making them difﬁcult, if not impossible to see. To maximize your observing, limit deep

sky viewing to

moonless nights far from the light polluted skies found around major urban areas. LPR ﬁlters enhance

deep sky viewing from light polluted areas by blocking unwanted light while transmitting light from cer-

tain deep sky objects. You can, on the other hand, observe planets and stars from light polluted areas or

when the Moon is out.

Seeing

Seeing conditions refers to the stability of the atmosphere and directly affects the amount of ﬁne detail

seen in extended objects. The air in our atmosphere acts as a lens which bends and distorts incoming

light rays. The amount of bending depends on air density. Varying temperature layers have different den-

sities and, therefore, bend light differently. Light rays from the same object arrive slightly displaced creat-

ing an imperfect or smeared image. These atmospheric disturbances vary from time-to-time and place-to-

place. The size of the air parcels compared to your aperture determines the “seeing” quality. Under good

seeing conditions, ﬁne detail is visible on the brighter planets like Jupiter and Mars, and stars are pinpoint

images. Under poor seeing conditions, images are blurred and stars appear as blobs.

The conditions described here apply to both visual and photographic observations.

Figure 5-3

Seeing conditions directly affect image quality. These drawings represent a point source (i.e., star)

under bad seeing conditions (left) to excellent conditions (right). Most often, seeing conditions

produce images that lie somewhere between these two extremes.

The AstroMaster LT series of telescopes was designed for visual observing. After looking at the night sky

for a while you may want to try your hand at photography of it. There are several forms of photography

possible with your telescope for celestial as well as terrestrial pursuits. Below is just a very brief discussion

of some of the methods of photography available and suggest you search out various books for detailed

information on the subject matter.

As a minimum you will need a digital camera or a 35mm SLR camera. Attach your camera to the telescope

with:

• Digital camera – you will need the Universal Digital Camera Adapter (# 93626). The adapter allows the

camera to be mounted rigidly for terrestrial as well as prime focus astrophotography.

• 35mm SLR camera – you will need to remove your lens from the camera and attach a T-Ring for your

speciﬁc camera brand. Then, you will need a T-Adapter (# 93625) to attach on one end to the T-Ring and

the other end to the telescope focus tube. Your telescope is now the camera lens.

SHORT EXPOSURE PRIME FOCUS PHOTOGRAPHY

Short exposure prime focus photography is the best way to begin imaging celestial objects. It is done by

attaching your camera to the telescope as described in the paragraph above. A couple of points to keep in

mind:

• Polar align the telescope and start the optional motor drive for tracking.

• You can image the Moon as well as the brighter planets. You will have to experiment with various

settings and exposure times. Much information can be obtained from your camera instruction manual

which can supplement what you can ﬁnd in detailed books on the subject matter.

• Do your photography from a dark sky observing site if possible.

PLANETARY & LUNAR PHOTOGRAPHY WITH SPECIAL IMAGERS

During the last few years a new technology has evolved which makes taking superb images of the planets

and moon relatively easy and the results are truly amazing. Celestron offers the NexImage (# 93712) which

is a special camera and included is software for image processing. You can capture planetary images your

ﬁrst night out which rivals what professionals were doing with large telescopes just a few short years ago.

CCD IMAGING FOR DEEP SKY OBJECTS

Special cameras have been developed for taking images of deep sky images. These have evolved over

the last several years to become much more economical and amateurs can take fantastic images. Several

books have been written on how to get the best images possible. The technology continues to evolve with

better and easier to use products on the market.

TERRESTRIAL PHOTOGRAPHY

Your telescope makes an excellent telephoto lens for terrestrial (land) photography. You can take images

of various scenic views, wildlife, nature, and just about anything. You will have to experiment with focusing,

speeds, etc. to get the best image desired. You can adapt your camera per the instructions at the top of

this page.

ASTROPHOTOGRAPHY

While your telescope requires little maintenance, there are a few things to remember that will ensure your

telescope performs at its best.

CARE AND CLEANING OF THE OPTICS

Occasionally, dust and/or moisture may build up on the objective lens or primary mirror depending on

which type of telescope you have. Special care should be taken when cleaning any instrument so as not to

damage the optics.

If dust has built up on the optics, remove it with a brush (made of camel’s hair) or a can of pressurized air.

Spray at an angle to the glass surface for approximately two to four seconds. Then, use an optical cleaning

solution and white tissue paper to remove any remaining debris. Apply the solution to the tissue and then

apply the tissue paper to the optics. Low pressure strokes should go from the center of the lens (or mirror)

to the outer portion. Do NOT rub in circles!

You can use a commercially made lens cleaner or mix your own. A good cleaning solution is isopropyl al-

cohol mixed with distilled water. The solution should be 60% isopropyl alcohol and 40% distilled water. Or,

liquid dish soap diluted with water (a couple of drops per one quart of water) can be used.

Occasionally, you may experience dew build-up on the optics of your telescope during an observing ses-

sion. If you want to continue observing, the dew must be removed, either with a hair dryer (on low setting)

or by pointing the telescope at the ground until the dew has evaporated.

If moisture condenses on the inside of the optics, remove the accessories from the telescope. Place the tele-

scope in a dust-free environment and point it down. This will remove the moisture from the telescope tube.

To minimize the need to clean your telescope, replace all lens covers once you have ﬁnished using it. Since

the cells are NOT sealed, the covers should be placed over the openings when not in use. This will prevent

contaminants from entering the optical tube.

Internal adjustments and cleaning should be done only by the Celestron repair department. If your tele-

scope is in need of internal cleaning, please call the factory for a return authorization number and price

quote.

COLLIMATION OF A NEWTONIAN

The optical performance of most Newtonian reﬂecting telescopes can be optimized by re-collimating (align-

ing) the telescope’s optics, as needed. To collimate the telescope simply means to bring its optical elements

into balance. Poor collimation will result in optical aberrations and distortions.

Before collimating your telescope, take time to familiarize yourself with all its components. The primary

mirror is the large mirror at the back end of the telescope tube. This mirror is adjusted by loosening and

tightening the three screws, placed 120 degrees apart, at the end of the telescope tube. The secondary mir-

ror (the small, elliptical mirror under the focuser, in the front of the tube) also has three adjustment screws

(you will need optional tools (described below) to perform collimation. To determine if your telescope

needs collimation ﬁrst point your telescope toward a bright wall or blue sky outside.

TELESCOPE MAINTENANCE

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Celestron AstroMaster LT 76AZ Owner's manual

Brand: Celestron

Model: AstroMaster LT 76AZ

Category: Telescopes

Type: Owner's manual

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